Several misunderstandings in steel shot selection

　　To ensure that the surface treatment is fully up to standard, the two core indicators of metal abrasives are: cleaning efficiency and consumption.

　　Several misunderstandings in steel shot selection: Are cast steel shots as round as possible? Are the more uniform the particle size, the better? Are the brighter the appearance, the better? Are cast steel shots as round as possible? Editor's answer: No. In the process of granulation to make steel shots, the molten steel cools from liquid to solid, and shrinks during the cooling process. This shrinkage is carried out in a free state, and there is no riser like a cast casting to replenish the part of the volume reduced after shrinkage. Therefore, elliptical particles with concave surfaces appear. These particles have undergone sufficient shrinkage, and the shape is not round but the structure is dense. For steel shots that have not undergone sufficient shrinkage, the roundness is good, but the structure is not dense, and there are shrinkage and shrinkage. Internal defects such as shrinkage cavities. From the perspective of use effect, steel shots are not as round as possible. Steel shots are usually used in the cleaning field. The cleaning efficiency of steel shots with high roundness is lower than that of steel shots with good shrinkage. The energy of throwing and hitting is E=1/2mv2. The shrinkage rate of the roundness is good and the structure is dense. Therefore, for the same volume, the mass m is large, the impact energy is high, and it is not easy to break. On the contrary, the steel shot with good roundness has a non-dense structure, small particle mass, low kinetic energy, and is easy to break. In the market, the reason why most cast steel shots have good roundness and poor quality is that the production conditions of the manufacturers are limited, the diameter of the granulation pool is small (8-14 meters), and the drop from the centrifugal disk to the water surface is small (0.2-1 meter), that is, the width and height of the workshop are not enough, and it cannot guarantee that the liquid steel shot formed by centrifugation has enough cooling and shrinkage time. It enters the water instantly, the surface is cooled, and the roundness is good, but the interior has not yet solidified, resulting in shrinkage and shrinkage holes. The crushing rate of steel shots is high during use. The diameter of the granulation pool is only greater than 20 meters, and the molding drop is greater than two meters, in order to ensure that the steel shot is fully shrunk. Is the more uniform the particle size of the steel shot, the better? Editor's answer: No. In the field of cleaning, steel shot blasting or spraying the surface of the workpiece to be cleaned forms pits on the cleaned surface. Only when the pits overlap, the entire surface can be thoroughly cleaned. The more uniform the particle size of the steel shot, the longer it takes to overlap the pits. For steel shots with a certain particle size mixing ratio, large steel shots play a cleaning role, while small steel shots play a role in cleaning the gaps formed by large-size steel shots, which greatly shortens the shot blasting time, improves the surface quality of the blasting, and improves production efficiency. Is the brighter the appearance of cast steel shots, the better? Editor's answer: No. The high-carbon cast steel shots on the market are currently divided into primary quenching and secondary quenching. They are difficult to distinguish in terms of composition, hardness, and metallographic structure. However, the secondary quenched steel shots have fine grains and high fatigue life, while the primary quenched steel shots have coarse grains and low fatigue life. The Fe3O4 oxide film formed on the surface of the once-quenched steel shot is thinner because it has not been heated or quenched again, so it looks very bright; while the Fe3O4 film on the surface of the steel shot that has been treated with the second quenching treatment becomes thicker, does not reflect light, and looks dull. Therefore, the appearance of cast steel shot is not the brighter the better, but it is important to pay attention to whether it has been treated with the second quenching treatment.